Hydrogen is desirable as a source of energy because it burns cleanly in air producing water as a by-product. In order to enhance the desirability of hydrogen as a fuel source, particularly for mobile applications, it is desirable to increase the available hydrogen content per unit volume of storage. Presently, this is done by conventional means such as storage under high pressure, at thousands of pounds per square inch, cooling to a liquid state, or absorbing into a solid such as a metal hydride. Pressurization and liquification require relatively expensive processing and storage equipment.
Storing hydrogen in a solid material such as metal hydrides, provides volumetric hydrogen density which is relatively high and compact as a storage medium. Binding the hydrogen as a solid is desirable since it desorbs when heat is applied, thereby providing controllable desorption.
Rechargeable hydrogen storage devices have been proposed to facilitate the use of hydrogen. Such devices may be relatively simple and generally are simply constructed as a shell and tube heat exchanger where the heat transfer medium delivers heat for desorption. Such heat transfer medium is supplied in channels separate from the chamber which houses the hydrogen storage material. Therefore, when hydrogen release is desired, hot fluid may be circulated through the channels, in heat transfer relationship with the storage material, to facilitate release of the hydrogen. To recharge the storage medium, hydrogen may be pumped into the chamber and flow through the storage material while the heat transfer medium removes heat, thus facilitating the charging or hydrogenating process. An exemplary hydrogen storage material and storage device arranged to provide suitable heat transfer surface and heat transfer medium for temperature management is exemplified in U.S. Pat. No. 6,015,041.
Presently, magnesium and magnesium-based alloys are considered to be the highest capacity hydrogen storage material with some reversible performance. However, there is limitation in that such magnesium based materials take up hydrogen at very high temperature and high hydrogen pressure. In addition, hydrogenation of the storage material is typically impeded by surface oxidation of the magnesium.
Therefore, in response to the desire for an improved hydrogen storage system, the present invention provides an improved hydrogen system, composition, and method of operation.